This invention relates to an economical process for the direct reduction of organic carboxylic acids and esters derived from said acids to the corresponding aldehydes.
U.S. Pat. Nos. 3,935,265 describes a method for the direct reduction of aromatic esters to aromatic aldehydes by contacting the ester with alumina at a temperature from about 400.degree. C. to about 500.degree. C. and at ambient pressure. Contact time can be as low as about three seconds. The best conversion using methyl benzoate ester was 39 percent, providing selectivity to benzaldehyde of 37 percent. The reference teaches that combinations of alumina and transition metals such as chromia-alumina may also be acceptable.
Other known catalysts for benzoic acid hydrogenation by gaseous hydrogen include a copper/chromium-containing substance made by co-precipitating copper, chromium and manganese salts and pelletizing the resulting product with diatomaceous earth and CrO.sub.3 (Japan Kokai 75 111,034). Alkali metal oxides and zinc oxide catalysts have also been disclosed. p It is also known to treat alumina-containing catalysts at elevated temperatures of up to 1000.degree. C. in order to improve their selectivity towards production of aldehyde product.